test 7 Flashcards
One type of circuit control device which may be manual, automatic or multi-contact
A. fuse
B. breaker
C. switch
D. relay
B. breaker
What are the primary methods of controlling electrical power?
A. by using manual switches and rheostats
B. by using variable reactance and transformers
C. by using electronic switches, such as diodes, transistors thyratrons, and thyristors
D. all of the above
D. all of the above
Common method(s) of controlling electrical power with reactance
A. switching a tapped inductor
B. using a saturable reactor
C. by a matching transformer
D. A and B above
D. A and B above
A reactive device used in controlling electrical power by using two windings on a common iron core. The control winding is supplied with small dc-current which causes the reactance of large ac-winding to change accordingly.
A. tapped inductor
B. saturable reactor
C. auto transformer
D. LVDT
B. saturable reactor
A saturable reactor with regenerative feedback.
A. tapped inductor
B. auto transformer
C. LVDT
D. magnetic amplifier
D. magnetic amplifier
Thyratrons in industrial electronics refers to ____________.
A. a gas-filled diode
B. a vacuum tube
C. gas-filled triode
D. an electron triode
C. gas-filled triode
\An electronic switch that has the highest single-device current capacity and can withstand overloads better.
A. Thyristors
B. ignitrons
C. SCR
D. triac
B. ignitrons
A semiconductor, electronic switch that has the highest single-device current rating
A. thyristor
B. triac
C. SCR
D. Quadric
C. SCR
The purpose of installing thyrectors across the incoming power lines to the speed control system is to ___________
A. cause the motor to caution
B. protect drive circuits from high voltage transient surges
C. increase the counter emf
D. allow the field winding current to continue flowing
B. protect drive circuits from high voltage transient surges
Semiconductor devices equivalent to thyratrons are generally called
A. thyrector
B. thyristor
C. diac
D. ignitron
B. thyristor
Using electronic devices as switches, what is(are) the general methods of controlling electrical power?
A. phase control
B. zero-voltage switching
C. static switching
D. all of the above
D. all of the above
Which power control switching method that greatly generates RFI or EMI and is therefore limited to low-frequency applications?
A. phase control
B. zero-voltage switching
C. inverter control
D. static switching
A. phase control
One of the electronic semiconductor devices known as diac, function as
A. four terminal multi-directional switch
B. two terminal bi-directional switch
C. two terminal unidirectional switch
D. three terminal bi-directional switch
B. two terminal bi-directional switch
Which of the trigger diodes has the highest holding voltage?
A. bidirectional-trigger diac
B. bidirectional-diode-thyristor diac
C. Shockley diode
D. thyrector
A. bidirectional-trigger diac
General term of electronic devices used to control or trigger large-power switching devices.
A. thyristor
B. thyrector
C. break-over devices
D. triggering devices
C. break-over devices
A break-over device that is basically a diode.
A. thyristor
B. thyrector
C. thyratron
D. triggering diode
D. triggering diode
A four-element solid state device that combi9nes the characteristics of both diodes and transistors
A. varactor
B. zener diode
C. tunnel diode
D. SCR
D. SCR
The most popular thyristor used in electrical power controllers
A. SCR
B. triac
C. SCS
D. PUT
A. SCR
Find the two stable operating conditions of an SCR.
A. Conducting and non-conducting
B. Oscillating and quiescent
C. NPN conduction and PNP conduction
D. Forward conducting and reverse conducting
A. Conducting and non-conducting
How do you stop conduction during which SCR is also conducting?
A. remove voltage gate
B. increase cathode voltage
C. interrupt anode current
D. reduce gate current
C. interrupt anode current
How do we turn “ON” or trigger an SCR?
A. by making the gate (G) positive with respect to its cathode (K)
B. by making the gate (G) positive with respect to its anode (A)
C. by making the cathode more positive with respect to the anode
D. A and C above
A. by making the gate (G) positive with respect to its cathode (K)
What is true about SCRs after they are being switched “ON”?
A. The anode (A) to cathode (K) continues to conduct even if the gate triggering voltage is removed.
B. The gate (G) must be provided with the required holding current to continue its conduction.
C. A small holding voltage at the gate is required for a continuous conduction.
D. B and C above
A. The anode (A) to cathode (K) continues to conduct even if the gate triggering voltage is removed.
The voltage across the anode (A) and cathode (K) terminals of an SCR when conducting.
A. holding voltage
B. breakdown voltage
C. breakback voltage
D. trigger voltage
A. holding voltage
The minimum amount of current needed for an SCR to conduct continuously.
A. holding current
B. triggering current
C. threshold current
D. average sustaining current
A. holding current
What is(are) the condition(s) in triggering SCR?
A. The gate voltage must be equal to or greater than the triggering voltage.
B. The gate current must be equal to or greater than the triggering current.
C. The anode (A) must be positive with respect to the cathode.
D. all of the above
D. all of the above
The voltage decreased across the anode (A) and cathode (K) of an SCR from non-conducting state to conducting state.
A. holding voltage
B. forward breakdown voltage
C. triggering voltage
D. breakback voltage
D. breakback voltage
An SCR rated 10 A is used as the controlling switch in a circuit powered by 50Vdc. When the SCR fires ON, its anode (A) to cathode (K) voltage was observed to be 2 V. Calculate the breakback voltage of the SCR.
A. 25 Vdc
B. 32 Vdc
C. 41 Vdc
D. 48 Vdc
D. 48 Vdc
The needed voltage at the gate of an SCR before it conducts.
A. minimum-gate trigger voltage
B. maximum-gate trigger voltage
C. minimum-gate peak-inverse voltage
D. maximum-gate peak-inverse voltage
A. minimum-gate trigger voltage
What is(are) the gate limitation(s) of SCRs and triacs?
A. maximum-gate power dissipation
B. maximum-gate peak-inverse voltage
C. maximum-gate trigger current and voltage
D. all of the above
D. all of the above
How can we extend the rating of SCRs?
A. by external cooling
B. by external circuitry
C. by connecting them in series/parallel
D. all of the above
D. all of the above
Use of heat sinks, forced air, and water cooling are examples of external cooling in SCRs and other devices. Which of these is the only recommended to be used for the largest power dissipating device?
A. metal heat sinks
B. forced air
C. water cooling
D. A and B above
C. water cooling
How can we increase the forward-voltage blocking capability of SCRs?
A. by connecting them in series
B. by connecting them in parallel
C. by cascading them
D. by connecting back to back in parallel
A. by connecting them in series
In connecting two SCRs in series, during “OFF” state, the voltage source must be properly shared between them, but due to devices’ differences, there might be unequal voltages across each SCR. How do we equalize these voltages?
A. by installing a snubber circuit
B. by adding a gate-to-cathode resistor
C. by shunting a capacitor across the anode (A) and cathode (K) of each SCR
D. by using a blocking-equalizing resistor
D. by using a blocking-equalizing resistor
What is true regarding blocking-equalizing resistors in SCRs connected in series?
A. Blocking-equalizing resistors are shunted across each SCR.
B. The value of these resistors is about 10% of the value of the blocking resistance of the SCR it is shunted with.
C. These resistors increases the leakage current towards the load.
D. All of the above
D. All of the above
A circuit used for voltage equalization during ON-OFF switching action of SCRs in series.
A. snubber circuit
B. crow-bar
C. clipper
D. clamper
A. snubber circuit
When a high current is needed, SCRs are connected in parallel. The problem with paralleled SCRs is, when they are not perfectly matched, one will conduct first before the other and carries the full-load current that is for sure greater than its maximum rating. To avoid this situation, both SCRs should be turned ON at the same time. How can we do this?
A. by using high triggering gate voltage
B. by using a gate-triggering transformer
C. by using reactors
D. all of the above are possible
D. all of the above are possible
In controlling electrical power using phase control method with SCR/triac being the active device, what do we call the period of the cycle before the device switches to conduction?
A. trigger time
B. trigger delay time
C. firing frequency
D. firing delay angle
D. firing delay angle
How many times per second does an SCR is turned ON and OFF when it is operated in a full-wave phase control at a line frequency of 60 Hz?
A. 30 times
B. 60 times (HV)
C. 90 times
D. 120 times (FW)
D. 120 times (FW)
A three terminal device that behaves roughly like SCR, except that it can conduct current in either direction when at ON.
A. thyristor
B. SUS
C. SBS
D. GTO
C. SBS
What is the difference between a triac and a silicon bilateral switch (SBS)?
A. An SBS is usually used as breakover device, while a triac is a load controlling device.
B. An SBS is for low voltage applications, while a triac is generally for high voltage applications.
C. An SBS has better and stable symmetrical-firing voltage than a triac.
D. all of the above
D. all of the above
A triac can be triggered ON by the application of a
A. positive voltage at the gate with respect to MT1
B. negative voltage at the gate with respect to MT1
C. positive or negative gate voltage with respect to MT2
D. all of the above are correct
D. all of the above are correct
Which are the three terminals of a TRIAC?
A. Gate, anode 1 and anode 2
B. Gate, source and sink
C. Base, emitter and collector
D. Emitter, base 1 and base 2
A. Gate, anode 1 and anode 2
What are the three terminals of a triac?
A. anode 1 (A1), anode 2 (A2) and gate (G)
B. mainterminal 1 (MT1), mainterminal 2 (MT2), and gate (G)
C. anode (A), cathode (K) and gate (G)
D. both A and B are acceptable
D. both A and B are acceptable
A silicon bilateral switch may be considered as s small power triac, and has three terminals namely,
A. anode 1 (A1), anode 2 (A2) and gate (G)
B. mainterminal 1 (MT1), mainterminal 2 (MT2), and gate (G)
C. anode (A), cathode (K) and gate (G)
D. both A and B are acceptab
D. both A and B are acceptable